1. Field of the Invention
The present invention relates to the process of fabricating integrated devices. More specifically, the present invention relates to a method and an apparatus that uses ellipsometric evaluation to determine layer thickness and composition of an integrated device.
2. Related Art
It is common practice in semiconductor factories to monitor layer thickness and composition of the various layers during fabrication of integrated devices such as integrated circuits, discrete electronic devices, Micro ElectroMechanical Systems (MEMS), optical components, materials using silicon-germanium (SiGe) and silicon-germanium-carbon (SiGeC), and other materials and devices. This monitoring is required to ensure that the integrated device will accurately perform its designed function.
Current methods of monitoring process steps during device fabrication include Rutherford back-scattering (RBS) and secondary ion mass spectrometry (SIMS). While these methods adequately measure the thickness and composition of the layer being examined, they both have drawbacks, which render them impractical for use in a production environment.
RBS can take several days to complete and can cost $50.00-$100.00 per sample. This cost is prohibitive. However, the delay of several days can be more significant. During the several day delay while the test is being completed, the production process may produce several million dollars worth of product. If the thickness and composition of a layer are not correct, all of this product may be defective. SIMS may take as long and costs even more per sample and therefore further aggravates the situation.
Hence, what is needed is a method and an apparatus for determining layer thickness and composition that is both economical and provides feedback in a commercially reasonable amount of time.